A nurse in Dallas, Texas, has become the first person to contract Ebola inside the United States. The nurse helped care for Ebola patient Thomas Eric Duncan, who died last week. Thomas Frieden, director of the Centers for Disease Control and Prevention, said the exact cause of transmission is unknown.

Thomas Frieden: “We don’t know what occurred in the care of the index patient, the original patient in Dallas. But at some point there was a breach in protocol. And that breach in protocol resulted in this infection.”

The case has raised concerns hospitals are not adequately protecting workers from Ebola. According to the union National Nurses United, 76 percent of 2,000 nurses surveyed said their hospitals had not communicated any policy to them regarding admission of potentially infected patients. The union has threatened to picket hospitals if nurses are not given protections including Hazmat suits and hands-on training.